Delta-Sigma ADCs Interface Easily To Sensors

Don Tuite | Jul 20, 2005

The LTC2480 delta-sigma analog-to-digital converters (ADCs) from Linear Technology feature a front-end design that can be driven directly from bridges, resistance-temperature detectors (RTDs), thermocouples, and other high-impedance sensors. This eliminates the drawbacks of on-chip buffering.

When summed over the entire conversion cycle, the total differential input current is zero, independent of the differential input voltage, common-mode input voltage, reference voltage, or output code. This lets circuit designers place external RC networks with large time constants directly in front of the ADC without degrading its dc accuracy.

The LTC2480 provides 16-bit resolution with 2-ppm INL, 1-ppm offset, and 15-ppm full-scale errors. It features an internal temperature sensor and programmable gain up to 256, suiting it for temperature compensation of low-level sensors. The LTC2482 comes without the internal temperature sensor or programmable gain. And, the LTC2484 provides 24-bit resolution and includes the temperature sensor, but it does not have programmable gain.

All three parts are pin-compatible in 3- by 3-mm, 10-pin DFN packaging. Additionally, they're screened for commercial and industrial temperature ranges. Pricing begins at $1.85 each for the LTC2480, $1.65 each for the LTC2482, and $2.45 each for the LTC2484. All prices are based on quantities of 1000 pieces.